Wavelength converting system

ABSTRACT

An embodiment of the invention discloses a wavelength converting system. The wavelength converting system comprises: a wavelength converter having a first area and a second area; a first light source disposed under the first area and inducing a first mixed light being visible above the first area; a second light source disposed under the second area and inducing a second mixed light being visible above the second area; and a carrier supporting the first light source and the second light source. The first light source and the second light source have a dominant wavelength difference of 1 nm˜20 nm, and the first mixed light and the second mixed light have a color temperature difference less than 100K.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 12/219,084, entitled “Wavelength convertingsystem”, filed on Jul. 16, 2008 for which priority is claimed under 35U.S.C. §120; and this application claims priority of Application No.096126269 filed in Taiwan on Jul. 18, 2007 under 35 U.S.C. §119, theentire contents of all of which are hereby incorporated by reference.

TECHNICAL FIELD

The invention relates to a wavelength converting system and moreparticularly to a wavelength converting system capable of generating awavelength spectrum having a stable color temperature in response to achange of the excitation wavelength.

DESCRIPTION OF BACKGROUND ART

Light-emitting diode (LED) is known by its high energy efficiency and sointroduced to the energy-saving movement in many kinds of equipments ofvariable fields including outdoor lighting, means of transportation, andhousehold lighting, such as street light, traffic light, outdoordisplay, headlamp, trail light, center high mounted stop lamps (CHMSL),and decoration light.

A basic structure of a light-emitting diode chip mainly includes a p-njunction. The hole of the p-type semiconductor material and the electronof the n-type semiconductor recombine to emit light under a biasvoltage. The light-emitting area in the structure is sometimes called“active layer” or “light-emitting layer”. The wavelength from thelight-emitting layer is determined by the adopted material. Thestructure emitting red light is constructed by introducing a mainmaterial such as GaP, GaAsP, AlGaAs, and AlGaInP. The structure emittinggreen light is constructed by introducing a main material such GaP andZnCdSe. The structure emitting blue light is constructed by introducinga main material such as SiC and GaN. Those different materials areusually grown on different substrates such as GaP, GaAs, SiC, andsapphire.

The available light-emitting diode chip in market emits not only whitelight but also variable color lights of almost the whole range of thevisible wavelength (400 nm˜750 nm) and ultraviolet. White light can begenerated in several ways such as by mixing lights from blue, green, andred chips, exciting phosphor by UV light, exciting phosphor by bluelight, using semiconductor wavelength converting material (also called“photo-recycling semiconductor LED”; PRS LED), and dye. The most commoncommercial way of generating white light makes yttrium aluminum garnet(YAG) phosphor be pumped by blue light to generate a complementarycolor. For example, a 460 nm blue chip is introduced to excite YAG:Cephosphor to generate a 570 nm around yellow light, one may control theconcentration and the thickness of the phosphor to adjust the ratio ofblue light to yellow light in order to produce white lights havingvarious color temperatures.

Phosphor absorbs shorter wavelengths to emit longer wavelengths, thatis, absorbs a high energy level radiation to emit a low energy levelradiation. A phosphor is characterized by its excitation band andemission band. The excitation band has a primary wavelength distributionshorter than that of the emission band, while the two bands may overlapin part. The peak wavelength difference of the absorption band and theemission wavelength is called “Stokes shift”. The phosphor may be causedto radiate in a similar emission spectrum by any wavelength within theexcitation band. However, the phosphor is operated at differentefficiencies responsive to different absorbed wavelengths, which dependson the composition of phosphor.

In another aspect, the numerous chips on a wafer appear to be in anon-uniform wavelength distribution spanning from 10 nm to 20 nm ormore. Provided a specific recipe of phosphor is introduced to directlyor indirectly overlay on or be packaged with all chips, the colortemperature of the white light from the end product is divergent sosignificantly that the qualitative uniformity of the application productis affected.

As shown in FIG. 1A, LED light source 12 emits blue lights 11 and 13 atspecific wavelengths. The blue light 13 excites phosphor 14 to generateyellow light 15. The blue light 11 and the yellow light 15 are mixedinto white light 17. The yellow light 15 is going to remain in the samespectrum even if the wavelength of the blue light from the LED lightsource 12 is changed but still within the excitation band of thephosphor 14. The wavelength difference of the blue light thereforeresults in a shift of the color temperature of the mixed white light 17.

In addition, a CIE chromaticity diagram is shown in FIG. 1B. A 460 nmblue light and a 571 nm yellow light generated by exciting YAG phosphorat a fixed condition are mixed into a white light of about 6000K colortemperature. However, if the blue light wavelength shifts up to 470 nmor down to 450 nm, while the yellow light is unchanged, the colortemperature of the mixed white light also shifts to 10000K or 5000K,which is usually unacceptable to common applications. To produce colorlights having constant color temperatures, therefore, the chips arenecessarily undergone sorting and binning processes before a condition-or characteristic-specific phosphor is applied to.

SUMMARY OF THE DISCLOSURE

A wavelength converting system in accordance with one embodiment ofpresent comprises: a wavelength converter having a first area and asecond area; a first light source disposed under the first area andinducing a first mixed light being visible above the first area; asecond light source disposed under the second area and inducing a secondmixed light being visible above the second area; and a carriersupporting the first light source and the second light source. The firstlight source and the second light source have a dominant wavelengthdifference of 1 nm˜20 nm, and the first mixed light and the second mixedlight have a color temperature difference less than 100K.

A wavelength converting system in accordance with one embodiment ofpresent invention comprises a first light-emitting diode chip, driven ona first current, having a first area and a first dominant wavelength; asecond light-emitting diode chip, driven on a second current, having asecond area and a second dominant wavelength different from the firstdominant wavelength; a wavelength converter disposed on the firstlight-emitting diode chip and the second light-emitting diode chip; anda mixed light, induced by the first light-emitting diode chip and thesecond light-emitting diode chip, being visible above the wavelengthconverter. The first current and the second current are configured tooppositely change in a range, and the mixed light has a colortemperature variation less than 100K within the range.

A wavelength converting system in accordance with one embodiment ofpresent invention comprises a plurality of light-emitting structureshaving a dominant wavelength distribution spanned in few nanometers ortens of nanometers; a trench formed between two of the plurality of thelight-emitting structures; and a wavelength converter disposed on theplurality of light-emitting structures and the trench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a conventional wavelength converting systemand its CIE chromaticity diagram.

FIG. 2A illustrates an excitation and emission spectrum of a YAGphosphor in accordance with an embodiment of present invention.

FIG. 2B illustrates an excitation and emission spectrum of a silicatephosphor in accordance with an embodiment of present invention.

FIG. 2C illustrates a CIE chromaticity diagram of a wavelengthconverting system in accordance with an embodiment of present invention.

FIG. 3 illustrates a wavelength converting system in accordance withanother embodiment of present invention.

FIG. 4 illustrates a wavelength converting system in accordance withfurther embodiment of present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments are described hereinafter in accompany with drawings.

In one embodiment of present invention, YAG and silicate-based phosphorsare selected to blend into a mixed phosphor (hereinafter called“mixture”, but the kinds and the quantities of materials are not limitedby the aforementioned.) In the embodiment, FIG. 2A illustrates thespectrum of YAG phosphor, which has an excitation spectrum of a range of200 nm˜530 nm, a principle emission spectrum of a range of 480 nm˜700nm, and a peak wavelength of about 530 nm. FIG. 2B illustrates thespectrum of the silicate-based phosphor, which has an excitationspectrum in a range of 300 nm˜500 nm, a principle emission spectrum of arange of 470 nm˜650 nm, and a peak wavelength of about 525 nm.

As shown in FIGS. 2A and 2B, YAG phosphor has a higher efficiency atabout 470 nm, while silicate-based phosphor has a higher efficiency atabout 450 nm. When the excitation wavelength moving from 470 nm to 450nm, the efficiency of YAG phosphor decreases, while the efficiency ofsilicate-based phosphor increases. In other words, provided the twophosphors are mixed and excited at a wavelength starting from 470 nm to450 nm, the ratio of the shorter wavelength fluorescent lightcontributed by silicate-based phosphor to the total fluorescent lightincreases, while the ratio of the longer wavelength fluorescent lightcontributed by YAG phosphor to the total fluorescent light decreases. Inconsequence, the ratio of the emission lights from YAG andsilicate-based phosphors changes with the variation of the excitation.In the embodiment, when the excitation wavelength decreasing, thewavelength spectrum of the mixed light from the mixture is slanted tothe direction of the shorter wavelength, i.e. the shorter wavelength isgiven a higher weighting in the mixed light. The color temperature ofthe color light resulting from mixing the emission light of the mixtureand the excitation light is kept in a constant range. On the contrary,when the excitation wavelength moving from the shorter wavelength to thelonger wavelength, the fluorescent mixture according to the embodimentis able to provide an emission light shifting to longer wavelength. Bymeans of the mixture according to the embodiment, a positive correlationis found between the emission wavelength and the excitation wavelength.

FIG. 2C shows a CIE chromaticity diagram illustrating the relationshipbetween the excitation light and the emission light or wavelengthconverting system in accordance with one embodiment of the invention.The lines respectively connecting the representative excitationwavelength and the representative emission wavelength of one and theother phosphor of the mixture, or any two kinds of phosphors, areintersected in the diagram. The arc of the lower left sector of theintersection represents the wavelength range of the excitation light.The arc of the upper right sector of the intersection represents thewavelength range of the emission light from the excited phosphor. Thechromaticity coordinates of the color light mixed by the emission lightand the unconverted excitation light locates on or nearby theintersection on the CIE diagram. The color temperature resulted from thewavelength converting system can be restricted on the vicinity of theline intersection by a well modification of the distribution of theexcitation wavelength and the phosphor ratio of the mixture. Therefore,the color light generated by the system can be kept on a relative stablecolor temperature. Specifically, applying the fluorescent mixtureaccording the embodiment to blue LED chips having divergent wavelengthsor spectra, one can obtains white lights with less variation by mixingthe yellow light generated by exciting the mixture by the light fromthose chips and the raw blue light from the same.

In the diagram, the line connecting 450 nm and 569 nm illustrates thepossible color light from the pure silicate-based phosphor, and the lineconnecting 470 nm and 573 nm illustrates the possible color light fromthe pure YAG phosphor. The two lines intersect at the point of the whitelight of around 6000 K. With a specific mixture ratio and arrangement ofYAG and silicate-based phosphors, the emission light having a dominantwavelength of 569 nm˜573 nm can be generated by the excitation lightranging between 450 nm and 470 nm, and mixed with the same to emit whitelight having a substantially constant color temperature around 6000 K.

As shown in FIG. 3, another embodiment of the invention discloses acarrier 22, light-emitting structures 24, and a phosphor 26 overlayingon the light-emitting structures 24, wherein the quantity of thelight-emitting structures is illustrative and not used to limit thedisclosure of the embodiment. The carrier 22 includes but not limited toa growth substrate and a material or a structure applicable to disposethe light-emitting structures 24. The wavelength of the light-emittingstructures 24 varies in a range of few nanometers, tens of nanometers,or applicable to the phosphor 26, for example, 10 nm˜20 nm. The dominantwavelength of the light-emitting structure 24 is within the visiblelight spectrum such as 420 nm˜480 nm, or the wavelength viable to excitethe phosphor 26. The light-emitting structures 24 on the carrier 22 canemit light in a wavelength distribution of Gaussian distribution ornon-normal distribution. The wavelength of the emission light of thephosphor 26 moves in a tendency following the change of the wavelengthof the excitation light. Even the light-emitting structures 24 haveexcitation wavelengths different from each other; the emissionwavelength from the phosphor 26 on the light-emitting structure 24 maybe spontaneously adjusted by following or tracing the shifting tendencyof the excitation wavelength, or according to the alteration of theexcitation wavelength. Accordingly, the impact, caused by the qualitydeviation such as the variation of the wavelength of the light-emittingstructure 24, on the color difference of the mixed light or theperceived color light quality can be reduced. For example, using thephosphor 26 of present embodiment, the color temperature of the colorlight mixed by the excitation light of the light-emitting structure 24and the emission light of the phosphor 26 can be kept in a fixed range.The range is determined by the kinds of phosphors, the user's requiringspecification, and/or the application environment.

In the drawings, the arrangement of overlaying the phosphor 26 is onlyan illustration of the embodiment. Any kinds of methods can apparentlybe used to dispose the phosphor 26 on the light-emitting structure 24,such as partial coverage, uniform thickness, varying thickness, upperside coverage, and lateral direction coverage. In one case, thelight-emitting structure 24 is grown on a growth substrate and coveredby the phosphor 26. In another case, the light-emitting structure 24 isseparated from a growth substrate, mounted on the carrier 22, and thencovered by the phosphor 26. Taiwan granted patent No. 1241728 and U.S.patent application Ser. No. 11/160,588 owned by the same applicant arehereby incorporated by reference. In further case, the light-emittingstructure 24 is a light-emitting diode chip or package, and the carrier22 is a circuit board. In addition, the light-emitting structure 24 canbe arranged on the carrier 22 in a flip-chip arrangement and thencovered by the phosphor 26. In a preferable case, the phosphor 26overlays on a light-pervious substrate or a light-pervious opticalelement. The light-emitting structure 24 preferably emits light in arange of 400 nm˜500 nm. The color light mixed by the excitation light ofthe light-emitting structure 24 and the emission light of the phosphor26 includes but not limited to white light and other visible light.

As shown in FIG. 4, in accordance with another embodiment of theinvention, a wavelength converting system 30 includes a first lightsource 32A, a second light source 32B, and a wavelength converter 34.The first light source 32A and the second light source 32B are able toemit light rays which show perceivable difference in wavelength,spectrum, or intensity. For example, the perceivable difference is awavelength difference or spectrum shift in a range of 1 nm˜20 nm or so.The wavelength converter 34 includes at least one material having acomposition able to be excited by the first light source 32A and thesecond light source 32B, and emitting light in response to a changingtendency of the excitation light in a specific spectrum, or in apositive correlation with the excitation light.

The wavelength converter 34 is excited by light 31B from the first lightsource 32A to generate emission light 31C. The unconverted light 31Afrom the first light source 32A and the light 31B are mixed to mixedlight 35A. The wavelength converter 34 is excited by light 33B from thesecond light source 32B to generate emission light 33C. The unconvertedlight 33A from the second light source 32B and the light 33C are mixedto mixed light 35B. The mixed lights 35A and 35B have similar colortemperature, for example, the mixed lights 35A and 35B have a colortemperature difference less than 100K, or a number below that an user isnot easily aware of such difference, or similar chromaticitycoordinates. Using the wavelength converter 34 in accordance withpresent embodiment, the system 30 can generate uniform or similar colorlights, such as the mixed lights 35A and 35B, even though there exists aperceivable wavelength difference between light sources such as lightsources 32A and 32B.

In present embodiment, the wavelength converter 34 may directly contactwith the light sources 32A and 32 b, for example, a package, includingmore light-emitting diode chips, is packaged by a material having afluorescent mixture showing a positive correlation between theexcitation wavelength and the emission wavelength. The wavelengthconverter 34 may also be separated from the light sources 32A and 32B,for example, a luminous device includes more light sources and alight-pervious optical element which is a kind of covering means such asa lampshade, a tube, a lens, a cover, a sticker, a plate, and a film,and covered by, coupled to, or mixed with the wavelength converter 34positioned on the light path of the light source and used to convert theoriginal wavelength of the light source. In addition, the wavelengthconverter 34 can be optionally formed on a reflective inner surface ofthe luminous device, and used to convert the light coming from the lightsource and then reflected by the inner surface, or being reflected totransmit the wavelength converter 34.

Table 1 shows an experimental result obtained by implementing anembodiment of the invention. Two 15 mil×15 mil nitride-serieslight-emitting diode chips are operated under controllable current andpositioned adjacent to each other in a package equipped with a silverreflector. Among the two chips, one has a dominant wavelength of 450 nm,and the other one has a dominant wavelength of 470 nm. Thesilicate-based phosphor and YAG phosphor in a weight ratio of about 1.08(0.26 g/0.24 g) are mixed with epoxy and disposed on the twolight-emitting diode chips. The input currents to the respective twolight-emitting diode chips are controlled to oppositely change in arange between 0 mA˜20 mA, i.e. the current inputted into one chip ariseswhile the current inputted into the other chip drops. The wavelengthspectrum of the mixed light resulted from the two chips can be changedby adjusting the currents into the chips. The configuration of theexperiment is used to simulate the wavelength distribution of blue lightranged in 450 nm˜470 nm. In one experimental case, the input current isset to levels of 0 mA, 5 mA, 10 mA, 15 mA, and 20 mA. One can observethat the correlated color temperature (CCT) of the resulted mixed lightcan be kept within 5945K˜6035K, wherein the difference is less than100K, even though the input currents of the two chips change. In otherwords, the fluorescent mixture in accordance with the embodiment of theinvention has a higher tolerance to the difference of the intensity andthe wavelength of the light sources such that the system can achieve arelative steady luminous quality.

Using the wavelength converter in accordance with an embodiment of theinvention, a user can have an opportunity to freely adopt any one chipfrom a single wafer. In other words, even there exists an emittingwavelength difference between the light-emitting diode chips on thesingle wafer, those chips, provided well functioning, can potentially beused in downstream products without further binning and sorting.

Furthermore, using the wavelength converter in accordance with anembodiment of the invention, even though the light sources arranged inthe wavelength converting system have divergent wavelengthdistributions, the color temperature resulted from the system is onlyslightly influenced by those property-divergent light sources.

Besides YAG and silicate-based phosphors adoptable in the embodiment ofthe invention, the material of the phosphor excitable to emit yellowlight includes but not limited to Terbium Aluminum Garnet (TAG) whichhas an exemplary composition of Tb₃Al₅O₁₂:Ce and oxynitride which has anexemplary composition of (SrBa)Si₂N₂O₂:Eu.

The foregoing description has been directed to the specific embodimentsof this invention. It will be apparent; however, that other variationsand modifications may be made to the embodiments without escaping thespirit and scope of the invention.

1. A wavelength converting system, comprising: a wavelength converterhaving a first area and a second area; a first light source disposedunder the first area and inducing a first mixed light being visibleabove the first area; a second light source disposed under the secondarea and inducing a second mixed light being visible above the secondarea; and a carrier supporting the first light source and the secondlight source; wherein the first light source and the second light sourcehave a dominant wavelength difference of 1 nm˜20 nm, and the first mixedlight and the second mixed light have a color temperature differenceless than 100K.
 2. The wavelength converting system of claim 1, furthercomprising a light-pervious optical element covering the first lightsource and the second light source, and being covered by, coupled to, ormixed with the wavelength converter.
 3. The wavelength converting systemof claim 2, wherein the light-pervious optical element is selected fromthe group consisting of a lampshade, a tube, a lens, a cover, a sticker,a plate, and a film.
 4. The wavelength converting system of claim 1,wherein the wavelength converter is separated from the first lightsource and the second light source.
 5. The wavelength converting systemof claim 1, wherein the wavelength converter is configured to directlycontact with the first light source and the second light source.
 6. Thewavelength converting system of claim 1, wherein the wavelengthconverter comprises a fluorescent mixture showing a positive correlationbetween an excitation wavelength and an emission wavelength.
 7. Thewavelength converting system of claim 1, wherein the first light sourceand the second light source are flip-chip mounted on the carrier.
 8. Thewavelength converting system of claim 1, wherein each of the first lightsource and the second light source comprises a light-pervious substrateor a light-pervious optical element.
 9. The wavelength converting systemof claim 8, wherein the wavelength converter is disposed on thelight-pervious substrate or the light-pervious optical element.
 10. Thewavelength converting system of claim 1, wherein the wavelengthconverter comprises two phosphors substantially having the sameprinciple emission spectrum.
 11. A wavelength converting system,comprising: a first light-emitting diode chip, driven on a firstcurrent, having a first area and a first dominant wavelength; a secondlight-emitting diode chip, driven on a second current, having a secondarea and a second dominant wavelength different from the first dominantwavelength; a wavelength converter disposed on the first light-emittingdiode chip and the second light-emitting diode chip; and a mixed light,induced by the first light-emitting diode chip and the secondlight-emitting diode chip, being visible above the wavelength converter;wherein the first current and the second current are configured tooppositely change in a range, and the mixed light has a colortemperature variation less than 100K within the range.
 12. Thewavelength converting system of claim 11, wherein the first area issubstantially equal to the second area.
 13. The wavelength convertingsystem of claim 11, wherein the range is between 0 mA˜20 mA.
 14. Thewavelength converting system of claim 11, further comprising a packagefor accommodating the first light-emitting diode chip and the secondlight-emitting diode chip.
 15. The wavelength converting system of claim11, wherein a ratio of the first current to the first area is differentfrom a ratio of the second current to the second area.
 16. Thewavelength converting system of claim 11, wherein the wavelengthconverter comprises a YAG phosphor.
 17. The wavelength converting systemof claim 11, wherein the wavelength converter comprises a silicate-basedphosphor.
 18. A wavelength converting system, comprising: a plurality oflight-emitting structures having a dominant wavelength distributionspanned in few nanometers or tens of nanometers; a trench formed betweentwo of the plurality of the light-emitting structures; and a wavelengthconverter disposed on the plurality of light-emitting structures and thetrench.
 19. The wavelength converting system of claim 18, wherein thedominant wavelength distribution comprises a Gaussian distribution or anon-normal distribution.
 20. The wavelength converting system of claim18, wherein the dominant wavelength distribution comprises a range of420 nm˜480 nm.